The present invention generally relates to packaging of semiconductor devices, and more particularly to a packaged semiconductor device that can be produced at a reduced cost.
With the progress of fabrication processes of semiconductor devices, the integration density of integrated circuits formed on a semiconductor chip is increasing continuously. With the increase in the integration density, the packages used for accommodating the semiconductor chip also are required to have a capability of providing a large number of interconnections leads in correspondence to the increased number of terminals on the chip.
FIG. 1 shows a conventional package 10 of the so-called QFP (quad flat package) type wherein a number of leads 11 are provided along the side of a package body 12. The leads 11 project laterally in the outward direction from the package body 12 and are bent downwardly. Further, the leads 11 are bent again in the horizontal direction and form the terminals 11a that extend laterally from the body 12. Thereby, a so-called gull-wing type terminal is formed. Obviously, this type of package, having the leads along the side wall of the package body, has a problem of insufficient location for providing the interconnection leads and is not suitable for accommodating semiconductor devices having a large integration density. Further, this type of package tends to exhibit variations in the vertical levels of the terminal parts 11a of the leads 11. Generally, the level of the terminal 11a may change as much as 100 .mu.m. However, such a large variation in the level of the terminal is not desirable from the view point of enabling reliable interconnections.
In order to avoid the problem pertinent to the package of FIG. 1, a so-called PGA (pin grid array) package is proposed as shown in FIG. 2, wherein a large number of interconnection pins 21 are arranged in rows and columns on the bottom surface of a package body 22. Thereby, one can increase the number of leads on the package body 22 dramatically. For example, leads of as many as several tens in number can be provided without difficulty. This PGA package, on the other hand, has a problem in that a process for embedding the pins 21 in the package body 22 is necessary. Generally, this process includes processes of introducing a large number of minute metal rods on a package body, and than to shake the body until the metal rods are settled in the holes formed thereby in the package body, as the pins 21. After the pins are settled, it is necessary to fix the pins on the package body 22. Thus, the process for fabricating the PGA package is time consuming and increases the cost of the device.